Recently, miniaturized and multiplexed analysis devices for disease diagnosis as well as genomics generate intense research interest in nano/micro technology-based bio applications. One of the major methods for multiplexing is based on distinguishable particles-based suspension in which each type of probe biomolecules such as protein and deoxyribonucleic acid (DNA) is immobilized.
Many encoding and decoding methods have been developed to attach a unique probe biomolecule to a unique particle in suspension and to detect the target molecule. For example, a diagnostic device using color-coded bead suspension, which contains polystyrene microbeads embedded in red and orange fluorescent dyes at different ratios for yielding distinctive colors, has been already commercialized by the incorporation of flow cytometry technology. The color code is decoded with reflected color image excited by a laser.
Alternatively, a recently developed suspension platform for biosensing uses multi-segmented nanowires, which are fabricated by alternating electrodeposition within a porous template with different metals such as gold (Au), silver (Ag) and copper (Cu) for the respective segments, as “barcodes” for the multiplexing. The barcode is decoded with the difference in optical reflectance of gold and silver segments.
Both of the two representative biosensing technologies, which use suspensions of color-coded microbeads and barcoded nanowires respectively, require laser-based instrumentation, a charge-coupled device (CCD) camera and image processing software for decoding and thus suffer from disadvantages in miniaturization and cost-effectiveness. In addition, the optical detection of nanowires is extremely difficult because nanowire diameters are on the limit of optical detection by a normal microscope. Moreover, it is not so easy to distinguish the barcode segments in these nanowires due to the interference crisis.
On the other hand, magnetic planar tags using an optical-magnetic characteristic in a soft magnetic material have disadvantages because the low remanence magnetization and the information coded on the planar tags may be erased due to small unwanted external magnetic fields. Decoding the information on the planar tags requires optical detection which is expensive to procure.
In order to overcome these disadvantages and to develop sufficiently miniaturized, multiplexed and cost-effective biosensing systems, a novel encoding and decoding method is required.